A well may be completed and brought into production, in part, by running a downhole oilfield tool comprising a perforation gun into the wellbore and firing the perforation gun. The perforation gun comprises explosive charges which, when ignited, pierce any wellbore casing and create a plurality of perforation tunnels in the formation surrounding the wellbore. Thereafter hydrocarbons may flow from the formation into the perforation tunnels, into the wellbore, and then rise up the wellbore to be produced at the surface.
The energy delivered by the explosive charges to the formation creates debris and may shatter the formation proximate to the perforation tunnels. Under some conditions, this debris may, to some extent, clog and/or block the perforation tunnels. It may be desirable, under some conditions, to provide for a surge of fluid into the downhole oilfield tool to encourage a flushing operation that will flush or sweep at least part of the debris out of the perforation tunnels. A surge chamber contained in the downhole oilfield tool comprising an enclosed volume of fluid or gas at a pressure lower than the wellbore pressure may be suddenly opened after the perforation gun has been fired, providing for a surge of wellbore fluids into the surge chamber, creating a transient under pressure in the wellbore that is less than the formation pressure. The pressure differential between the formation and the wellbore may cause fluid flow from the formation into the wellbore, flushing and/or sweeping the debris out of the perforation tunnels and clearing the perforation tunnels.
In some wellbores, multiple production zones may be contemplated. In this case, the downhole oilfield tool may comprise more than one perforation gun. The perforation guns may be separated by one or more spacer sub-assemblies that displace the perforation guns by a distance corresponding to the distance between the several production zones. In some cases, a plurality of perforation guns may be coupled to each other to extend the perforation zone of a single production zone.